This invention relates to curable polymers which are usable as materials for electrolytes to be used in electrochemical elements such as batteries, capacitors, sensors, display devices and recording devices and electrolytes using these polymers.
It has been a practice to use liquids as electrolytes in electrochemical elements such as batteries, capacitors, sensors, display devices and recording devices. When used or stored over a long time, however, liquid electrolytes sometimes suffer from leakage, thus showing poor reliability.
In recent years, mobile personal computers and mobile phones have widely spread and thus it has been required to enlarge the capacity of secondary batteries. Thus, attempts have been widely made to develop lithium ion nonaqueous secondary batteries with enlarged capacity which are now mainly employed as small-size secondary batteries. However, it is unavoidable that batteries comprising low-molecular weight solvent (e.g., ethylene carbonate, propylene carbonate, diethyl carbonate, etc.) suffer from liquid-leakage.
On the other hand, researches and developments have been vigorously made on solid electrolytes in order to solidify electrolytes to thereby prevent liquid-leakage, thus giving highly reliable elements. At present, polyethylene oxide (hereinafter referred to simply as PEO), its derivatives and composites thereof with alkali metal salts are well known as organic solid electrolytes. However, PEO composites are frequently crystallized and thus fail to achieve high conductivity. To solve this problem, JP-A-63-76273 discloses a crosslinked polymeric solid electrolyte obtained by reacting a polyether having a hydroxyl group with a diacrylate (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). However, this electrolyte is still insufficient in conductivity, i.e., about 10xe2x88x924S/cm at room temperature. Moreover, a secondary battery using this electrolyte is still insufficient in discharge capacity at low temperatures. In addition, it is required to use a strong base in the crosslinking reaction to synthesize the above-mentioned electrolyte. It is therefore desired to develop an electrolyte which can be obtained under mild reaction conditions.
An object of the present invention is to provide crosslinked polymers which are useful as electrolytic materials. Another object thereof is to provide electrolytes with high ion conductivity by using these crosslinked polymers. Further object thereof is to provide a process for producing electrolytes with high ion conductivity under mild conditions by using crosslinked polymers.
An still further object of the present invention is to provide secondary batteries by using solid electrolytes which have high ion conductivity and are easy to handle. Additional object thereof is to provide secondary batteries which are free from liquid-leakage and show excellent discharge properties at low temperatures.
The present inventors have conducted intensive studies and, as a result, developed the following crosslinked polymers, electrolytes using the crosslinked polymers and nonaqueous secondary batteries using the electrolytes, thus successfully achieving the above-mentioned objects of the present invention.
(1) A crosslinked polymer which is obtained by a crosslinking reaction between a compound having at least two substituents, in total, of at least one kind selected from the group consisting of xcex1,xcex2-unsaturated sulfonyl, xcex1,xcex2-unsaturated nitryl and xcex1,xcex2-unsaturated carbonyl groups in its molecule and a compound having at least two nucleophilic groups in its molecule.
(2) An electrolyte containing a crosslinked polymer, which is obtained by a crosslinking reaction between a compound having at least two substituents, in total, of at least one kind selected from the group consisting of xcex1,xcex2-unsaturated sulfonyl, xcex1,xcex2-unsaturated nitryl and xcex1,xcex2-unsaturated carbonyl groups in its molecule and a compound having at least two nucleophilic groups in its molecule, and a salt.
(3) A process for producing an electrolyte comprising reacting a compound having at least two substituents, in total, of at least one kind selected from the group consisting of xcex1,xcex2-unsaturated sulfonyl, xcex1,xcex2-unsaturated nitryl and xcex1,xcex2-unsaturated carbonyl groups in its molecule with a compound having at least two nucleophilic groups in its molecule in a salt or an organic solvent in which the salt is dissolved.
(4) A nonaqueous secondary battery having a positive electrode, a negative electrode and an electrolyte, wherein said electrolyte is one comprising a crosslinked polymer, which is obtained by a crosslinking reaction between a compound having at least two substituents, in total, of at least one kind selected from the the group consisting of xcex1,xcex2-unsaturated sulfonyl, xcex1,xcex2-unsaturated nitryl and xcex1,xcex2-unsaturated carbonyl groups in its molecule and a compound having at least two nucleophilic groups in its molecule, a an organic solvent.